Internet DRAFT - draft-ietf-netconf-adaptive-subscription

draft-ietf-netconf-adaptive-subscription







NETCONF Working Group                                              Q. Wu
Internet-Draft                                                   W. Song
Intended status: Experimental                                     Huawei
Expires: 14 June 2024                                             P. Liu
                                                            China Mobile
                                                                   Q. Ma
                                                                  Huawei
                                                                 W. Wang
                                                           China Telecom
                                                                  Z. Niu
                                                               Microsoft
                                                        12 December 2023


               Adaptive Subscription to YANG Notification
              draft-ietf-netconf-adaptive-subscription-04

Abstract

   This document defines a YANG data model and associated mechanism that
   enable adaptive subscription to a publisher's event streams.  The
   periodic update interval for the event streams can be set adaptively.
   Applying these elements allows servers to automatically adjust the
   rate and volume of telemetry traffic sent from a publisher to
   receivers.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 14 June 2024.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Model Overview  . . . . . . . . . . . . . . . . . . . . . . .   5
     2.1.  Subscription Configuration  . . . . . . . . . . . . . . .   6
     2.2.  YANG RPC  . . . . . . . . . . . . . . . . . . . . . . . .   8
       2.2.1.  "establish-subscription" RPC  . . . . . . . . . . . .   9
     2.3.  Notifications for Adaptive Subscribed Content . . . . . .  10
   3.  XPath Complexity Evaluation . . . . . . . . . . . . . . . . .  10
   4.  Adaptive Subscription YANG Module . . . . . . . . . . . . . .  12
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     5.1.  Updates to the IETF XML Registry  . . . . . . . . . . . .  17
     5.2.  Updates to the YANG Module Names Registry . . . . . . . .  18
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   7.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  19
   8.  Acknowledges  . . . . . . . . . . . . . . . . . . . . . . . .  19
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  21
   Appendix A.  Example YANG Module  . . . . . . . . . . . . . . . .  21
     A.1.  "example-wifi-network-diagnostic" YANG Module . . . . . .  22
   Appendix B.  Adaptive Subscription and Notification Example . . .  26
     B.1.  "edit-config" Example . . . . . . . . . . . . . . . . . .  27
     B.2.  Create Adaptive Subscription Example  . . . . . . . . . .  29
     B.3.  "xpath-evaluation-unsupported" error response example . .  29
     B.4.  "adaptive-period-update" notification example . . . . . .  30
   Appendix C.  Changes between Revisions  . . . . . . . . . . . . .  31
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  34

1.  Introduction

   YANG-Push subscriptions [RFC8641] allow subscriber applications to
   request a continuous customized stream of updates from a YANG
   datastore without needing to poll.  It defines a mechanism (i.e.,
   update trigger) to determine when an update record needs to be
   generated.  Two types of subscription are introduced in [RFC8641],
   distinguished by how updates are triggered: periodic and on-change.




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   *  Periodic subscription allows subscribed data to be streamed to the
      destination at a configured fixed periodic interval;

   *  On-change subscription allows update to be triggered whenever a
      change in the subscribed information is detected.

   However, in some large-scale deployments where an increased data
   collection rate is used, it becomes more likely that both clients and
   servers could be temporarily overwhelmed with a burst of streamed
   data, and network and computation resources could be excessively
   consumed.  Therefore, it may be expensive to continuously monitor
   operational data at a high collection rate.  Conversely, if the rate
   at which we collect a stream of data is set too low or low priority
   telemetry data is chosen to be dropped, these telemetry data will not
   be sufficient to detect and diagnose problems and to verify correct
   network behavior.

   There is a need for a service to balance between data management cost
   and real-time streaming telemetry.  To achieve this, servers can be
   configured with multiple different period intervals and corresponding
   subscription update policies which allow servers/publishers to
   automatically switch to different period intervals according to the
   network condition changes without the interaction with the client for
   policy update instructions.  Take wireless network performance
   monitoring as an example, when the wireless signal strength falls
   below a configured threshold, the subscribed data can be streamed at
   a higher rate to capture potentially important data and events (e.g.,
   continuous service degeneration); while when the wireless signal
   strength crosses a configured threshold, the subscribed data can be
   streamed at a lower rate.  Another case to consider is to balance the
   impact of continuous streaming updates on the CPU utilization of the
   device.  When the CPU utilization on the device exceeds a certain
   high-level value, it might be desired for the monitoring service to
   specify a less rapid period interval to make room to save more
   resources.  Conversely, When the CPU usage is lower than the
   specified threshold, a shorter period interval may be used without
   exhausting the CPU resources at the same time.

   A client might choose to monitor the operational state and send a
   request to modify the data collection rate on the server as needed.
   But how often the client evaluates if the modification of the data
   collection rate is required highly depends on the current collection
   rate, collecting a stream of data at a low rate prevents the
   subscriber from capturing sufficient data for timely decision-making.
   In addition, when tens of thousands of network devices need to be
   managed, frequent follow-up modification requests are prone to
   errors.




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   This document defines a YANG data model and associated mechanism that
   enable adaptive subscription to a publisher's event streams.  The
   periodic update interval for the event streams can be set adaptively.
   Applying these elements allows servers to automatically adjust the
   rate and volume of telemetry traffic sent from a publisher to
   receivers.

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The following terms are defined in [RFC5277], [RFC7950], [RFC3198],
   [RFC8342], [RFC8639], [RFC8641] and are not redefined here:

   *  Event

   *  Client

   *  Configuration

   *  Configured subscription

   *  Configuration datastore

   *  Notification message

   *  Publisher

   *  Receiver

   *  Subscriber

   *  Subscription

   *  On-change subscription

   *  Periodic subscription

   *  Selection filter

   This document defines the following term:

   Adaptive Subscription:  A subscription that specifies subscription




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      period update policy on the servers when the subscription is
      initialized and allows servers/publishers to automatically switch
      to different period intervals according to network condition
      changes without interacting with the client for update policy
      instructions.

2.  Model Overview

   This document defines a YANG data model named "ietf-adapt-
   subscription" which augments the "update-trigger" choice defined in
   the "ietf-yang-push" module [RFC8641] with subscription configuration
   parameters that are specific to a subscriber's adaptive subscription.

   In addition to subscription state notifications defined in [RFC8639]
   and notifications for subscribed content defined in [RFC8641], "ietf-
   adapt-subscription" module also defines "adaptive-period-update"
   notification to report the update interval change.

   The following tree diagrams [RFC8340] provide an overview of the data
   model for "ietf-adapt-subscription" module.

 module: ietf-adapt-subscription
   augment /sn:subscriptions/sn:subscription/yp:update-trigger:
     +--:(adaptive-periodic)
        +--rw adaptive-periods
           +--rw adaptive-period* [name]
              +--rw name                   yang:yang-identifier
              +--rw xpath-eval-criterion   yang:xpath1.0
              +--rw period                 yp:centiseconds
              +--rw anchor-time?           yang:date-and-time
   augment /sn:establish-subscription/sn:input/yp:update-trigger:
     +--:(adaptive-periodic)
        +-- adaptive-periods
           +-- adaptive-period* [name]
              +-- name                   yang:yang-identifier
              +-- xpath-eval-criterion   yang:xpath1.0
              +-- period                 yp:centiseconds
              +-- anchor-time?           yang:date-and-time
   augment /sn:modify-subscription/sn:input/yp:update-trigger:
     +--:(adaptive-periodic)
        +-- adaptive-periods
           +-- adaptive-period* [name]
              +-- name                   yang:yang-identifier
              +-- xpath-eval-criterion   yang:xpath1.0
              +-- period                 yp:centiseconds
              +-- anchor-time?           yang:date-and-time
   augment /sn:subscription-started/yp:update-trigger:
     +--:(adaptive-periodic)



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        +-- adaptive-periods
           +-- adaptive-period* [name]
              +-- name                   yang:yang-identifier
              +-- xpath-eval-criterion   yang:xpath1.0
              +-- period                 yp:centiseconds
              +-- anchor-time?           yang:date-and-time
   augment /sn:subscription-modified/yp:update-trigger:
     +--:(adaptive-periodic)
        +-- adaptive-periods
           +-- adaptive-period* [name]
              +-- name                   yang:yang-identifier
              +-- xpath-eval-criterion   yang:xpath1.0
              +-- period                 yp:centiseconds
              +-- anchor-time?           yang:date-and-time

   notifications:
     +---n adaptive-period-update
        +--ro id?                                     sn:subscription-id
        +--ro period                                  yp:centiseconds
        +--ro period-update-time?                     yang:date-and-time
        +--ro datastore                               identityref
        +--ro (selection-filter)?
           +--:(by-reference)
           |  +--ro selection-filter-ref
                      selection-filter-ref
           +--:(within-subscription)
              +--ro (filter-spec)?
                 +--:(datastore-subtree-filter)
                 |  +--ro datastore-subtree-filter?
                            <anydata> {sn:subtree}?
                 +--:(datastore-xpath-filter)
                    +--ro datastore-xpath-filter?
                            yang:xpath1.0 {sn:xpath}?

2.1.  Subscription Configuration

   For adaptive subscriptions, triggered updates will occur at the
   boundaries of specified time intervals when the corresponding trigger
   condition is satisfied.  These boundaries can be calculated from the
   following adaptive periodic parameters:

   *  a "name" represents the name of each adaptive period;









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   *  a "period" defines the duration between push updates, in units of
      0.01 seconds.  The "period" has the same definition as the
      yp:period for periodic subscription defined in [RFC8641], while it
      must be present with an "xpath-eval-criterion" parameter so that
      update interval can be switched based on trigger conditions
      indicated by the "xpath-eval-criterion" parameter;

   *  an "anchor-time"; update intervals fall on the points in time that
      are a multiple of a "period" from an "anchor-time".  If an
      "anchor-time" is not provided, then the "anchor-time" MUST be set
      with the creation time of the initial update record inside each
      periodic timeframe.

   *  an "xpath-eval-criterion" represents a standard XPath evaluation
      expression (See section 6.4 of [RFC7950]) that is applied against
      the targeted data node, which is used to trigger/control the
      update interval switching within the server.  It follows the rules
      defined in section 3.4 of [XPATH1.0] and contains a comparison of
      a targeted node instance to the specific threshold in the XPath
      format.  Different from selection filter defined in [RFC8641], it
      monitors a specific data node instance change and evaluates the
      trigger condition associated with the specified threshold value to
      be true or false using XPath rules and does not affect the even/
      update record output generation from a publisher.  The updates are
      only pushed as the corresponding period interval when the XPath
      expression is evaluated to "true".

      It is not always trivial for a subscriber to determine the
      threshold used in an XPath expression criterion.  Sometimes the
      threshold needs to be adjusted during the lifecycle of an adaptive
      subscription, depending on historical fluctuation range and how
      rapid the targeted value of the node changes, distribution
      characteristics of the targeted node value or even the generated
      volume of telemetry traffic.

      How often the XPath expression criterion is evaluated to decide
      whether to switch to another period interval is up to the
      publisher's implementation.  With minimal delay, the expression
      can be evaluated whenever changes to targeted data node occur, or
      at the end of each shortest streaming update period.  To reduce
      the frequency of evaluation, the server can choose to check
      targeted node change at every multiple (e.g.,2 or 3) high-
      frequency streaming update periods.

      The represented expression defined in "xpath-eval-criterion" is
      evaluated in the following XPath context:





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      -  The set of namespace declarations is the set of prefix and
         namespace pairs for all YANG modules implemented by the server,
         where the prefix is the YANG module name and the namespace is
         as defined by the "namespace" statement in the YANG module.

      -  If the leaf is encoded in XML, all namespace declarations in
         scope on the "xpath-eval-criterion" leaf element are added to
         the set of namespace declarations.  If a prefix found in the
         XML is already present in the set of namespace declarations,
         the namespace in the XML is used.

      -  The set of variable bindings is empty.

      -  The function library is the core function library defined in
         [XPATH1.0] and the function defined in Section 10 in RFC 7950.

      -  The context node is the root node in the accessible tree which
         is the operational state data in the server.

      For the cases where the "xpath-eval-criterion" parameter refers to
      multiple list/leaf-list instances, XPath abbreviated syntax can be
      used to identify a particular instance, e.g., to represent a
      comparison for a leaf in a list entry:

        /if:interfaces/if:interface[if:name="eth0"]/if:in-errors>1000.

      The server MUST convert the XPath evaluation expression defined in
      "xpath-eval-criterion" to a boolean value and internally apply the
      "boolean" function defined in Section 4.3 in [XPATH1.0] if the
      evaluated result is not a boolean value.  It MUST evaluates to
      "false" if the target node instance to be compared is deleted.
      Only if the XPath expression is evaluated to "true", does the
      publisher switch to the corresponding period with which push
      updates are reported.

   Note that the adaptive subscription may not be supported by every
   YANG datastore node.  A publisher MAY decide to simply reject an
   adaptive subscription with "adaptive-unsupported" (defined in
   Section 2.2.1.1) if the scope of the subscription contains selected
   data nodes for which adaptive subscription is not supported.

2.2.  YANG RPC









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2.2.1.  "establish-subscription" RPC

   The augmentation of YANG module "ietf-yang-push" made to RPCs
   specified in YANG module "ietf-subscribed-notifications" [RFC8639] is
   introduced.  This augmentation concerns the "establish-subscription"
   RPC, which is augmented with parameters that are needed to specify a
   subscriber's adaptive subscriptions.  These parameters are the same
   as the ones defined in Section 2.1.

2.2.1.1.  RPC Failures

   As specified in [RFC8639] and [RFC8641], RPC error responses from the
   publisher are used to indicate a rejection of an RPC for any reason.
   This document introduces three new RPC errors for "establish-
   subscription" RPC.

   establish-subscription
   -----------------------------
   adaptive-unsupported
   xpath-evaluation-unsupported
   multi-xpath-criteria-conflict

   The "adaptive-unsupported" RPC error is used to indicate that the
   adaptive subscription is not supported for the targeted set of data
   nodes that are selected by the filter.

   The "xpath-evaluation-unsupported" RPC error is used to indicate that
   a server failed to parse syntax defined in "xpath-eval-criterion".
   The failure can be caused by either a syntax error or some XPath 1.0
   syntax not supported against the specific data node.

   When specified, multiple XPath evaluation criteria inside "adaptive-
   periods" container MUST be mutually exclusive.  The "multi-xpath-
   criteria-conflict" error is used to indicate that the multiple XPath
   evaluation criteria represented by "xpath-eval-criterion" are
   evaluated as conflicting, i.e., more than one condition expressions
   are evaluated to "true".  As the operational state on the device
   changes, multiple XPath evaluation criteria may also conflict with
   each other during the lifetime of an adaptive subscription, the
   publisher may still push updates at the shortest streaming period
   among multiple corresponding period intervals in such cases.

   For an example of how the above RPC errors can be returned, see the
   "xpath-evaluation-unsupported" error response illustrated in
   Appendix B.3.






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   Note that existing RPC errors defined in RFC 8639 and RFC 8641 are
   still supported by this document.  For example, if any configured
   period for adaptive subscription is not supported by the publisher, a
   "period-unsupported" error response could be used.

2.3.  Notifications for Adaptive Subscribed Content

   The adaptive update notification is similar to subscription state
   change notifications defined in [RFC8639].  It is inserted into the
   sequence of notification messages sent to a particular receiver.  As
   stated in RFC 8639, section 2.7, the adaptive update notification
   cannot be dropped or filtered out, it cannot be stored in replay
   buffers, and it is delivered only to impacted receivers of a
   subscription.  The identification of the adaptive update notification
   is easy to separate from other notification messages through the use
   of the YANG extension "subscription-state-notif".  This extension
   tags a notification as a subscription state change notification.

   The elements in the 'adaptive-period-update' notification include:

   *  a "period" that defines the duration between push updates, the
      period can be changed based on trigger conditions.

   *  a "period-update-time" that designates a timestamp when the server
      starts to switch to another period interval because the evaluated
      "xpath-eval-criterion" expression result changed.

   *  A selection filter to identify YANG nodes of interest in a
      datastore.  Filter contents are specified via a reference to an
      existing filter or via an in-line definition for only that
      subscription based on XPath evaluation criteria defined in section
      6.4 of [RFC7950].  Referenced filters allow an implementation to
      avoid evaluating filter acceptability during a dynamic
      subscription request.  The "case" statement differentiates the
      options.  Note that filter contents are not affected by the
      "xpath-eval-criterion" parameter defined by the update trigger.

3.  XPath Complexity Evaluation

   YANG-Push subscriptions [RFC8641] specify selection filters to
   identify targeted YANG datastore nodes and/or datastore subtrees for
   which updates are to be pushed.  In addition, it specifies update
   policies which contain conditions that trigger generation and pushing
   of new update records.  To support a subscriber's adaptive
   subscription defined in this document, the trigger condition also
   uses similar selection filters to express a standard XPath evaluation
   criterion (section 6.4 of [RFC7950]) that is applied against the
   targeted data node(s).



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   The following complex implementation and use choices need to be
   cautious, although they have already been well supported by the
   section 3.4 of [XPATH1.0]:

   *  Support XPath evaluation criteria for all "config true" and
      "config false" data nodes;

   *  Support more than one target data node selection and operation
      (e.g., addition, subtraction, division and multiplication) in a
      single XPath evaluation criterion;

   *  Support any type of node value in the XPath evaluation criterion,
      e.g., string, int64, uint64, and decimal64 types;

   *  Both objects in the XPath evaluation criterion to be compared are
      node-sets;

   *  Targeted data to be compared are in different data types, e.g.,
      one is an integer, the other is a string.

   As described in section 6.4 of [RFC7950], Numbers in XPath 1.0 are
   IEEE 754 [IEEE754-2008] double-precision floating-point values; some
   values of int64, uint64, and decimal64 types cannot be exactly
   represented in XPath expressions.

   If targeted data to be compared are in different data types, a
   conversion function is needed to convert different data types into
   numbers.

   If both objects in XPath evaluation criteria to be compared are node-
   sets, more computation resources are required which add complexity.

   To reduce these complexities, the following implementation and use
   principles are recommended:

   *  XPath evaluation criteria are applied against a minimal set of
      data nodes in the data model, the minimal set of data nodes can be
      advertised using "ietf-notification-capabilities" module defined
      in [RFC9196];

   *  Both targets in the XPath evaluation criterion to be compared are
      in the same data type;

   *  One target to be compared in the XPath evaluation criterion is a
      leaf/leaf-list data node with numerical data type (e.g., signed/
      unsigned integer) and the other is a numerical threshold value.





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   If a server receives an XPath evaluation criterion with some XPath
   syntax unsupported against the specific targeted data node, an RPC
   error with "xpath-evaluation-unsupported" MUST be returned.

4.  Adaptive Subscription YANG Module

   This YANG module makes imports from [RFC8639], [RFC8641] and
   [I-D.ietf-netmod-rfc6991-bis].

   <CODE BEGINS> file "ietf-adapt-subscription@2023-12-13.yang"
      module ietf-adapt-subscription {
        yang-version 1.1;
        namespace "urn:ietf:params:xml:ns:yang:ietf-adapt-subscription";
        prefix as;

        import ietf-subscribed-notifications {
          prefix sn;
          reference
            "RFC 8639: Subscription to YANG Notifications";
        }
        import ietf-yang-push {
          prefix yp;
          reference
            "RFC 8641: Subscription to YANG Notifications for Datastore
             Updates";
        }
        import ietf-yang-types {
          prefix yang;
          reference
            "RFC YYYY: Common YANG Data Types";
        }

        organization
          "IETF NETCONF (Network Configuration) Working Group";
        contact
          "WG Web:   <http://tools.ietf.org/wg/netconf>
           WG List:  <netconf@ietf.org>

           Editor: Qin Wu
                 <mailto:bill.wu@huawei.com>

           Editor: Wei Song
                 <mailto: songwei80@huawei.com>

           Editor: Peng Liu
                 <mailto: liupengyjy@chinamobile.com>

           Editor: Qiufang Ma



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                 <mailto: maqiufang1@huawei.com>

           Editor: Wei Wang
                <mailto: wangw36@chinatelecom.cn>

           Editor: Zhixiong Niu
                <mailto: Zhixiong.Niu@microsoft.com>";
        description
          "This module extends the YANG data module defined in
           YANG-push to enable the subscriber's adaptive
           subscriptions to a publisher's event streams with various
           different period intervals to report updates.

           Copyright (c) 2023 IETF Trust and the persons identified
           as authors of the code. All rights reserved.

           Redistribution and use in source and binary forms, with
           or without modification, is permitted pursuant to, and
           subject to the license terms contained in, the Revised
           BSD License set forth in Section 4.c of the IETF Trust's
           Legal Provisions Relating to IETF Documents
           (https://trustee.ietf.org/license-info).

           This version of this YANG module is part of RFC xxxx
           (https://www.rfc-editor.org/info/rfcxxxx); see the RFC
           itself for full legal notices.

           The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
           'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
           'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
           are to be interpreted as described in BCP 14 (RFC 2119)
           (RFC 8174) when, and only when, they appear in all
           capitals, as shown here.";

        revision 2023-12-13 {
          description
            "Initial revision";
          reference
            "RFC xxxx: Adaptive Subscription to YANG Notification.";
        }

        identity adaptive-unsupported {
          base sn:establish-subscription-error;
          description
            "Adaptive-subscription is not supported for the targeted set
             of objects that are selectable by the filter.";
        }




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        identity xpath-evaluation-unsupported {
          base sn:establish-subscription-error;
          description
            "Unable to parse the xpath evaluation criteria defined in
             'xpath-eval-criterion' because of a syntax error or some
             XPath 1.0 syntax not supported against the specific
             data node.";
        }

        identity multi-xpath-criteria-conflict {
          base sn:establish-subscription-error;
          base sn:subscription-terminated-reason;
          description
            "Multiple Xpath evaluation criteria represented by
             'xpath-eval-criterion' are evaluated as a conflict. I.e.,
             more than one condition expression is evaluated to
             'true'.";
        }

        grouping adaptive-subscription-modifiable {
          description
            "This grouping describes the datastore-specific adaptive
             subscription conditions that can be changed during the
             lifetime of the subscription.";
          container adaptive-periods {
            list adaptive-period {
              key "name";
              description
                "An entry in this list represents an adaptive period
                 which defines a push update interval and trigger
                 conditions to switch to the update interval for
                 sending an event record to the subscriber.";
              leaf name {
                type yang:yang-identifier;
                description
                  "The name of adaptive period.";
              }
              leaf xpath-eval-criterion {
                type yang:xpath1.0;
                mandatory true;
                description
                  "An XPath string, representing a logical expression,
                   which can contain comparisons of datastore values
                   and logical operations in the XPath format.";
              }
              leaf period {
                type yp:centiseconds;
                mandatory true;



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                description
                  "Duration of time that should occur between periodic
                   push updates, in units of 0.01 seconds.";
              }
              leaf anchor-time {
                type yang:date-and-time;
                description
                  "Designates a timestamp before or after which a series
                   of periodic push updates is determined.  The next
                   update will take place at a point in time that is a
                   multiple of a period from the 'anchor-time'.
                   For example, for an 'anchor-time' that is set for the
                   top of a particular minute and a period interval of a
                   minute, updates will be sent at the top of every
                   minute that this subscription is active.";
              }
            }
            description
              "Container for adaptively periodic subscription.";
          }
        }

        augment "/sn:subscriptions/sn:subscription/yp:update-trigger" {
          description
            "This augmentation adds additional subscription parameters
             that apply specifically to adaptive subscription.";
          case adaptive-periodic {
            description
              "Defines adaptively periodic case for sending an event
               record to the subscriber.";
            uses adaptive-subscription-modifiable;
          }
        }

        augment
          "/sn:establish-subscription/sn:input/yp:update-trigger" {
          description
            "This augmentation adds additional establish-subscription
             parameters that apply specifically to datastore updates to
             RPC input.";
          case adaptive-periodic {
            description
              "Defines adaptively periodic case for sending an event
               record to the subscriber.";
            uses adaptive-subscription-modifiable;
          }
        }




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        augment "/sn:modify-subscription/sn:input/yp:update-trigger" {
          description
            "This augmentation adds additional modify-subscription
             parameters that apply specifically to datastore updates to
             RPC input.";
          case adaptive-periodic {
            description
              "Defines adaptively periodic case for sending an event
               record to the subscriber.";
            uses adaptive-subscription-modifiable;
          }
        }

        augment "/sn:subscription-started/yp:update-trigger" {
          description
            "This augmentation adds additional adaptive subscription
             parameters to the notification that a subscription has
             started.";
          case adaptive-periodic {
            description
              "Defines adaptively periodic case for sending an event
               record to the subscriber.";
            uses adaptive-subscription-modifiable;
          }
        }

        augment "/sn:subscription-modified/yp:update-trigger" {
          description
            "This augmentation adds additional adaptive subscription
             parameters to the notification that a subscription has been
             modified.";
          case adaptive-periodic {
            description
              "Defines adaptively periodic case for sending an event
               record to the subscriber.";
            uses adaptive-subscription-modifiable;
          }
        }

        notification adaptive-period-update {
          sn:subscription-state-notification;
          description
            "This notification contains a push update that in turn
             contains data subscribed to via a subscription.  In the
             case of a periodic subscription, this notification is sent
             for periodic updates.  It can also be used for
             synchronization updates of an on-change subscription.
             This notification shall only be sent to receivers of a



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             subscription.  It does not constitute a general-purpose
             notification that would be subscribable as part of the
             NETCONF event stream by any receiver.";
          leaf id {
            type sn:subscription-id;
            description
              "This references the subscription that drove the
               notification to be sent.";
          }
          leaf period {
            type yp:centiseconds;
            mandatory true;
            description
              "New duration of time that should occur between periodic
               push updates, in units of 0.01 seconds.";
          }
          leaf period-update-time {
            type yang:date-and-time;
            description
              "Designates a timestamp when the server starts to switch
               to another period interval because the evaluated 'xpath-
               external-eval' expression result changed.";
          }
          uses yp:datastore-criteria {
            refine "selection-filter/within-subscription" {
              description
                "Specifies the selection filter and where it originated
                 from.  If the 'selection-filter-ref' is populated, the
                 filter in the subscription came from the 'filters'
                 container.  Otherwise, it is populated in-line as part
                 of the subscription itself.";
            }
          }
        }
      }
   <CODE ENDS>

5.  IANA Considerations

5.1.  Updates to the IETF XML Registry

   This document registers one URI in the IETF XML registry [RFC3688].
   Following the format in [RFC3688], the following registration is
   requested to be made:







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   ---------------------------------------------------------------------
      URI: urn:ietf:params:xml:ns:yang:ietf-adapt-subscription
      Registrant Contact: The IESG.
      XML: N/A, the requested URI is an XML namespace.
   ---------------------------------------------------------------------

5.2.  Updates to the YANG Module Names Registry

   This document registers one YANG module in the YANG Module Names
   registry [RFC7950].  Following the format in [RFC6020], the following
   registration is requested to be made:

   ---------------------------------------------------------------------
      Name:         ietf-adapt-subscription
      Namespace:    urn:ietf:params:xml:ns:yang:ietf-adapt-subscription
      Prefix:       as
      Reference:    RFC xxxx
   ---------------------------------------------------------------------

6.  Security Considerations

   The YANG module specified in this document defines a schema for data
   that is designed to be accessed via network management protocols such
   as NETCONF [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF layer
   is the secure transport layer, and the mandatory-to-implement secure
   transport is Secure Shell (SSH) [RFC6242].  The lowest RESTCONF layer
   is HTTPS, and the mandatory-to-implement secure transport is TLS
   [RFC8446].

   The NETCONF Configuration Access Control Model (NACM) [RFC8341]
   provides the means to restrict access for particular NETCONF or
   RESTCONF users to a preconfigured subset of all available NETCONF or
   RESTCONF protocol operations and content.

   There are a number of data nodes defined in this YANG module that are
   writable/creatable/deletable (i.e., config true, which is the
   default).  These data nodes may be considered sensitive in some
   network environments.  Write operations (e.g., edit-config) to these
   data nodes without proper protection can have a negative effect on
   network operations.  These are the subtrees and data nodes and their
   sensitivity/vulnerability:

   *  /sn:subscriptions/sn:subscription/yp:update-trigger/as:adaptive-
      periods/as:adaptive-period/as:period

   *  /sn:subscriptions/sn:subscription/yp:update-trigger/as:adaptive-
      periods/as:adaptive-period/as:anchor-time




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   *  /sn:establish-subscription/sn:input/yp:update-trigger/as:adaptive-
      periods/as:adaptive-period/as:period

   *  /sn:establish-subscription/sn:input/yp:update-trigger/as:adaptive-
      periods/as:adaptive-period/as:anchor-time

7.  Contributors

   Thanks Michael Wang, Liang Geng for their major contributions to the
   initial modeling and use cases.

      Michael Wang
      Email: wangzitao@huawei.com

      Liang Geng
      China Mobile
      32 Xuanwumen West St, Xicheng District
      Beijing  10053

      Email: gengliang@chinamobile.com

8.  Acknowledges

   We would like to thank Rob Wilton, Thomas Graf, Andy Bierman, Michael
   Richardson, Henk Birkholz, Chong Feng, Adrian Farrel for valuable
   review on this document, special thanks to Thomas and Michael for
   organizing the discussion on several relevant drafts and reach the
   common understanding on the concept and ideas.  Thanks Michael for
   providing CHIP/Matter WIFI statistics reference.

9.  References

9.1.  Normative References

   [I-D.ietf-netmod-rfc6991-bis]
              Schönwälder, J., "Common YANG Data Types", Work in
              Progress, Internet-Draft, draft-ietf-netmod-rfc6991-bis-
              15, 23 January 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
              rfc6991-bis-15>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.






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   [RFC3198]  Westerinen, A., Schnizlein, J., Strassner, J., Scherling,
              M., Quinn, B., Herzog, S., Huynh, A., Carlson, M., Perry,
              J., and S. Waldbusser, "Terminology for Policy-Based
              Management", RFC 3198, DOI 10.17487/RFC3198, November
              2001, <https://www.rfc-editor.org/info/rfc3198>.

   [RFC5277]  Chisholm, S. and H. Trevino, "NETCONF Event
              Notifications", RFC 5277, DOI 10.17487/RFC5277, July 2008,
              <https://www.rfc-editor.org/info/rfc5277>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <https://www.rfc-editor.org/info/rfc7950>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
              <https://www.rfc-editor.org/info/rfc8342>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.







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   [RFC8639]  Voit, E., Clemm, A., Gonzalez Prieto, A., Nilsen-Nygaard,
              E., and A. Tripathy, "Subscription to YANG Notifications",
              RFC 8639, DOI 10.17487/RFC8639, September 2019,
              <https://www.rfc-editor.org/info/rfc8639>.

   [RFC8641]  Clemm, A. and E. Voit, "Subscription to YANG Notifications
              for Datastore Updates", RFC 8641, DOI 10.17487/RFC8641,
              September 2019, <https://www.rfc-editor.org/info/rfc8641>.

   [RFC9196]  Lengyel, B., Clemm, A., and B. Claise, "YANG Modules
              Describing Capabilities for Systems and Datastore Update
              Notifications", RFC 9196, DOI 10.17487/RFC9196, February
              2022, <https://www.rfc-editor.org/info/rfc9196>.

9.2.  Informative References

   [CHIP]     CSA, "Connected Home over IP Specification", April 2021.

   [IEEE754-2008]
              IEEE, "IEEE Standard for Floating-Point Arithmetic",  DOI
              10.1109/IEEESTD.2008.4610935, 2008,
              <http://standards.ieee.org/findstds/
              standard/754-2008.html>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [XPATH1.0] W3C, "https://www.w3.org/TR/1999/REC-xpath-19991116/", 11
              November 1999.

Appendix A.  Example YANG Module

   This section presents an example YANG module so that Appendix B can
   give examples of how the YANG module defined in Section 4 is used to
   perform adaptive subscription.  The example YANG module used in this
   section represents a Wi-Fi Network Diagnostics data specified in
   [CHIP] which can be used by a Node to assist a user or Administrative
   Node in diagnosing potential problems.



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   YANG tree diagram for the "example-wifi-network-diagnostic" module:

   module: example-wifi-network-diagnostic
     +--ro server
     |  +--ro bssid?                       yang:mac-address
     |  +--ro security-type?               enumeration
     |  +--ro wifi-version?                enumeration
     |  +--ro channel-num?                 int8
     |  +--ro rssi?                        int8
     |  +--ro beacon-lost-count?           int8
     |  +--ro beacon-rx-count?             int8
     |  +--ro packet-multicast-rx-count?   int8
     |  +--ro packet-multicast-tx-count?   int8
     |  +--ro packet-unicast-rx-count?     int8
     |  +--ro packet-unicast-tx-count?     int8
     |  +--ro current-max-rate?            int8
     |  +--ro overrun-count?               int8
     +--ro events
        +--ro event* [name]
           +--ro name                   string
           +--ro disconnection?         enumeration
           +--ro association-failure?   enumeration
           +--ro connection-status?     enumeration

A.1.  "example-wifi-network-diagnostic" YANG Module

   module example-wifi-network-diagnostic {
     yang-version 1;
     namespace "http://example.com/yang/wifi-network-diagnostic";
     prefix wnd;

     import ietf-yang-types {
       prefix yang;
     }

     container server {
       config false;
       description
         "Configuration of the WiFi Server logical entity.";
       leaf bssid {
         type yang:mac-address;
         description
           "The MAC address of a wireless access point.";
       }
       leaf security-type {
         type enumeration {
           enum unspecified {
             value 0;



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           }
           enum none {
             value 1;
           }
           enum wep {
             value 2;
           }
           enum wpa {
             value 3;
           }
           enum wpa2 {
             value 4;
           }
           enum wpa3 {
             value 5;
           }
         }
         description
           "The type of Wi-Fi security used. A value of 0
            indicate that the interface is not currently
            configured or operational.";
       }
       leaf wifi-version {
         type enumeration {
           enum 80211a {
             value 0;
           }
           enum 80211b {
             value 1;
           }
           enum 80211g {
             value 2;
           }
           enum 80211n {
             value 3;
           }
           enum 80211ac {
             value 4;
           }
           enum 80211ax {
             value 5;
           }
         }
         description
           "The highest 802.11 standard version usable
            by the Node.";
       }
       leaf channel-num {



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         type int8;
         description
           "The channel that Wi-Fi communication is currently
            operating on. A value of 0indicates that the interface
            is not currently configured or operational.";
       }
       leaf rssi {
         type int8;
         description
           "The RSSI of the Node's Wi-Fi radio in dBm.";
       }
       leaf beacon-lost-count {
         type int8;
         description
           "The count of the number of missed beacons the
            Node has detected.";
       }
       leaf beacon-rx-count {
         type int8;
         description
           "The count of the number of received beacons. The
            total number of expected beacons that could have been
            received during the interval since association SHOULD
            match the sum of BeaconRxCount and BeaconLostCount. ";
       }
       leaf packet-multicast-rx-count {
         type int8;
         description
           "The number of multicast packets received by
            the Node.";
       }
       leaf packet-multicast-tx-count {
         type int8;
         description
           "The number of multicast packets transmitted by
            the Node.";
       }
       leaf packet-unicast-rx-count {
         type int8;
         description
           "The number of multicast packets received by
            the Node.";
       }
       leaf packet-unicast-tx-count {
         type int8;
         description
           "The number of multicast packets transmitted by
            the Node.";



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       }
       leaf current-max-rate {
         type int8;
         description
           "The current maximum PHY rate of transfer of
            data in bytes-per-second.";
       }
       leaf overrun-count {
         type int8;
         description
           "The number of packets dropped either at ingress or
            egress, due to lack of buffer memory to retain all
            packets on the ethernet network interface. The
            OverrunCount attribute SHALL be reset to 0 upon a
            reboot of the Node..";
       }
     }
     container events {
       config false;
       description
         "Configuration of WIFI Network Diagnostic events.";
       list event {
         key "name";
         description
           "The list of event sources configured on the
            server.";
         leaf name {
           type string;
           description
             "The unique name of an event source.";
         }
         leaf disconnection {
           type enumeration {
             enum de-authenticated {
               value 1;
             }
             enum dis-association {
               value 2;
             }
           }
           description
             "A Node's Wi-Fi connection has been disconnected as a
              result of de-authenticated or dis-association and
              indicates the reason.";
         }
         leaf association-failure {
           type enumeration {
             enum unknown {



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               value 0;
             }
             enum association-failed {
               value 1;
             }
             enum authentication-failed {
               value 2;
             }
             enum ssid-not-found {
               value 3;
             }
           }
           description
             "A Node has attempted to connect, or reconnect, to
              a Wi-Fi access point, but is unable to successfully
              associate or authenticate, after exhausting all
              internal retries of its supplicant.";
         }
         leaf connection-status {
           type enumeration {
             enum connected {
               value 1;
             }
             enum notconnected {
               value 2;
             }
           }
           description
             "A Node's connection status to a Wi-Fi network has
              changed. Connected, in this context, SHALL mean that
              a Node acting as a Wi-Fi station is successfully
              associated to a Wi-Fi Access Point.";
         }
       }
     }
   }

Appendix B.  Adaptive Subscription and Notification Example

   The examples within this document use the normative YANG module
   "ietf-adapt-subscription" defined in Section 4 and the non-normative
   example YANG module "example-wifi-network-diagnostic" defined in
   Appendix A.1.

   This section shows some typical adaptive subscription and
   notification message exchanges.





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B.1.  "edit-config" Example

   The client configures adaptive subscription policy parameters on the
   server.  The adaptive subscription configuration parameters require
   the server to support two update intervals (i.e., 5 seconds, 60
   seconds) and report updates every 60 seconds if the rssi value is
   greater than or equal to -65dB; If the rssi value is less than -65dB,
   switch to 5 seconds period value to report updates.











































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  <rpc message-id="101"
    xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
    <edit-config>
     <target>
      <running/>
     </target>
     <config>
      <subscriptions
       xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
       xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
       <subscription>
       <id>1011</id>
       <yp:datastore
        xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
                ds:operational
       </yp:datastore>
       <yp:datastore-xpath-filter
        xmlns:wnd="http://example.com/yang/wifi-network-diagnostic">
               /wnd:server
       </yp:datastore-xpath-filter>
       <as:adaptive-periods
        xmlns:as="urn:ietf:params:xml:ns:yang:ietf-adapt-subscription">
        <as:adaptive-period>
         <as:name>adaptive-period-1</as:name>
         <as:xpath-eval-criterion>
          /wnd:server/wnd:rssi&lt;-65
         </as:xpath-eval-criterion>
         <as:period>5</as:period>
        </as:adaptive-period>
        <as:adaptive-period>
         <as:name>adaptive-period-2</as:name>
         <as:xpath-eval-criterion>
          /wnd:server/wnd:rssi&gt;=-65
         </as:xpath-eval-criterion>
         <as:period>60</as:period>
       </as:adaptive-period>
       </as:adaptive-periods>
       <receivers>
         <receiver>
          <name>host.example.com</name>
         </receiver>
       </receivers>
       </subscription>
      </subscriptions>
     </config>
    </edit-config>
   </rpc>




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B.2.  Create Adaptive Subscription Example

   The subscriber sends an "establish-subscription" RPC with the
   parameters listed in to request the creation of an adaptive
   subscription.  The adaptive subscription configuration parameters
   require the server to report updates every 5 seconds if the rssi
   value is less than -65dB; If the rssi value is greater than or equal
   to -65dB, switch to 60 seconds period value.  (Section 2)

    <netconf:rpc message-id="101"
     xmlns:netconf="urn:ietf:params:xml:ns:netconf:base:1.0">
     <establish-subscription
      xmlns="urn:ietf:params:xml:ns:yang:ietf-subscribed-notifications"
      xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
      <yp:datastore
       xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
              ds:operational
      </yp:datastore>
      <yp:datastore-xpath-filter
       xmlns:wnd="http://example.com/yang/wifi-network-diagnostic">
           /wnd:server
      </yp:datastore-xpath-filter>
      <as:adaptive-periods
       xmlns:as="urn:ietf:params:xml:ns:yang:ietf-adapt-subscription">
       <as:adaptive-period>
        <as:name>adaptive-period-1</as:name>
        <as:xpath-eval-criterion>
         /wnd:server/wnd:rssi&lt;-65
        </as:xpath-eval-criterion>
        <as:period>5</as:period>
       </as:adaptive-period>
       <as:adaptive-period>
        <as:name>adaptive-period-2</as:name>
        <as:xpath-eval-criterion>
         /wnd:server/wnd:rssi&gt;=-65
        </as:xpath-eval-criterion>
        <as:period>60</as:period>
       </as:adaptive-period>
      </as:adaptive-periods>
     </establish-subscription>
    </netconf:rpc>

B.3.  "xpath-evaluation-unsupported" error response example

   If the subscriber has authorization to establish the subscription
   with a server, but the server had not been able to fully satisfy the
   request from the subscriber, the server should send an RPC error
   response.



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   For instance, if the XPATH 1.0 syntax against the targeted data node
   defined in "xpath-eval-criterion" is not supported by the server' s
   implementation, the server returns a reply indicating a failure.  The
   following <rpc-reply> illustrates an example:

   <?xml version="1.0" encoding="utf-8"?>
   <rpc-reply message-id="101"
    xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <rpc-error>
       <error-type>application</error-type>
       <error-tag>invalid-value</error-tag>
       <error-severity>error</error-severity>
       <error-app-tag>
         ietf-adapt-subscription:xpath-evaluation-unsupported
       </error-app-tag>
       <error-path
         xmlns:wnd="http://example.com/yang/wifi-network-diagnostic">
         /wnd:server/wnd:rssi
       </error-path>
     </rpc-error>
   </rpc-reply>

   Since adaptive subscription allows a server to be configured with
   multiple different period intervals and corresponding XPath
   evaluation criteria to trigger update interval switch in the server,
   it may be possible for the server to return multiple <rpc-error>
   elements with "xpath-evaluation-unsupported" failure specified by
   different error paths.  The subscriber can use this information in
   future attempts to establish a subscription.

B.4.  "adaptive-period-update" notification example

   Upon the server switches from the update interval 5 seconds to the
   new update interval 60 seconds, before sending event records to
   receivers, the "adaptive-period-update" notification should be
   generated and sent to the receivers to inform the receivers that the
   update interval value is switched to the new value.














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   <notification
    xmlns="urn:ietf:params:xml:ns:netconf:notification:1.0"
    xmlns:yp="urn:ietf:params:xml:ns:yang:ietf-yang-push">
    <eventTime>2016-11-21T13:51:00Z</eventTime>
    <adaptive-period-update
     xmlns="urn:ietf:params:xml:ns:yang:ietf-adapt-subscription">
     <id>1011</id>
     <period>60</period>
     <yp:datastore
      xmlns:ds="urn:ietf:params:xml:ns:yang:ietf-datastores">
          ds:operational
     </yp:datastore>
     <yp:datastore-xpath-filter
      xmlns:wnd="http://example.com/yang/wifi-network-diagnostic">
          /wnd:server
     </yp:datastore-xpath-filter>
    </adaptive-period-update>
   </notification>

Appendix C.  Changes between Revisions

   This section is to be removed before publishing as an RFC.

   v03 -v04

   *  Add CPU utilization case in introduction section;

   *  Change the Xpath expression parameter "xpath-external-eval" to
      "xpath-eval-criterion";

   *  Some tweaks to the XPath Complexity Evaluation section;

   *  Editorial updates (e.g., fix long lines);

   v02 -v03

   *  Augment "modify-subscription", "subscription-started",
      "subscription-modified" to also support adaptive-subscription
      parameters;

   *  Replace the "anchor-time" parameter defined in adaptive-period-
      update notification with "period-update-time";

   *  Fix the YANG module and XML snippet errors in Appendix sections.

   v01 -v02

   *  Editorial changes to improve readability



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   *  Clarify that "period" and "xpath-external-eval" parameters must be
      co-exist so that the period can be switched based on trigger
      conditions indicated by "xpath-external-eval"

   v00 -v01

   *  Clarify what if multiple Xpath condition expressions conflict with
      each other during the lifecycle of an adaptive subscription

   *  Clarify that existing RPC errors defined in RFC 8639 and 8641 are
      still supported by this document

   *  Refine the YANG module: add contact information, fix IETF Trust
      Copyright statement, fix yanglint validation error

   v09 -v10

   *  Change the draft intended status to "experimental"

   *  Problem statement refinement

   v08 -v09

   *  Define two new RPC errors to report when adaptive subscription
      unsupported or multiple XPath criteria conflict.

   *  Remove the "watermark" parameter.

   *  Add clarification about how to evaluate the XPath expression
      defined in "xpath-external-eval".

   *  Add clarification about how to compare a targeted data object in a
      specific list entry.

   v07 -v08

   *  Define a new RPC error to report when an XPath syntax defined in
      "xpath-external-eval" is unsupported by a server.

   *  Add a new example showing how the RPC error being returned by a
      publisher.

   *  The usage examples fixed in the Appendix.

   *  Grammatical errors correction(missing articles, plurality
      mismatches, etc).

   v06 -v07



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   *  The usage examples typo fixed in the Appendix.

   *  Add reference to RFC7950 XPATH Evaluation section and XPATH 1.0

   *  Clarify the definitions of 'xpath-external-eval' and 'selection-
      filter' by reusing XPATH Evaluation rules in RFC7950.

   *  Add a new terminology "adaptive subscription".

   *  Add one section to discuss Arbitrary XPath Complexity.

   v05 -v06

   *  Replace example-wifi-mac module with example-wifi-network-
      diagnostic using WIFI statistics specified in CHIP specification.

   *  Update adaptive subscription Example to align with WIFI example
      module change.

   *  Add one more reference to CHIP Specification.

   v04 -v05

   *  Remove "modify-subscption" RPC usage.

   *  Module update to fix the nits.

   *  Update adaptive subscription Example.

   *  Other Editorial changes.

   v03 - v04

   *  Add missing subtrees and data nodes in the security section;

   *  Change "adaptive-update" notification into "adaptive-period-
      update" notification;

   *  Other Editorial changes.

   v02 - v03

   *  Clarify the difference between low priority telemetry data
      dropping and collection rate switching in the introduction
      section;






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   *  Update the abstract and introduction section to focus on
      collection rate switching in the server without interaction with
      the remote client;

   *  Format usage example and change ssid into rssi in the appendix;

   *  Use boilerplate and reuse the terms in the terminology section.

Authors' Addresses

   Qin Wu
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing
   Jiangsu, 210012
   China
   Email: bill.wu@huawei.com


   Wei Song
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing
   Jiangsu, 210012
   China
   Email: songwei80@huawei.com


   Peng Liu
   China Mobile
   32 Xuanwumen West St, Xicheng District
   Beijing
   Email: liupengyjy@chinamobile.com


   Qiufang Ma
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing
   Jiangsu, 210012
   China
   Email: maqiufang1@huawei.com


   Wei Wang
   China Telecom
   32 Xuanwumen West St, Xicheng District
   Beijing



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   Email: wangw36@chinatelecom.cn


   Zhixiong Niu
   Microsoft
   Email: Zhixiong.Niu@microsoft.com













































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